OBJECTIVE: to contribute to the validation of the (ECOHIS) by studying its psychometric properties when applied to a Portuguese preschool population. METHODS: Cross-sectional study conducted with children aged between three and five-years-old. The non-probabilistic sample included two preschools in the municipality of Lisbon. Children who agreed to participate and whose guardians signed the informed consent were included. Data collection included a questionnaire, administered to the parents, and an intraoral examination of the children. The questionnaire included the Portuguese version of ECOHIS. The intraoral examination included the caries diagnosis according to the World Health Organization criteria. Discriminant validity compared the ECOHIS score between children with and without caries experience (Mann-Whitney U-test). Cohen's d was calculated to estimate the magnitude of the difference. Reliability analysis included Cronbach's α and test-retest. Construct validity was analyzed by the correlation between the ECOHIS score and dmft (Spearman's correlation). A significance level of 5% was used. RESULTS: The sample included 104 children (mean age 4.1 years). ECOHIS values were significantly different between children with and without caries (p=0.004). The Cohen's d was 0.84. The Cronbach's was 0.78, with no significant increase in value when eliminating any of the items. The test-retest showed significant correlation (r=0.76; p=0.01). There was a significant correlation between the ECOHIS score and caries experience (r=0.28; p=0.004). CONCLUSION: The Portuguese version of the ECOHIS showed good psychometric properties, indicating that it is a reliable and valid tool to measure the impact of oral health in preschool children.